Re: [PATCH] [RFC] drm/i915: Handle HPD when it has actually occurred

["Jindal, Sonika" <sonika.jindal@xxxxxxxxx>]

On 7/6/2015 2:06 PM, Daniel Vetter wrote:
> On Mon, Jul 06, 2015 at 11:23:53AM +0530, Sonika Jindal wrote:
> > Writing to PCH_PORT_HOTPLUG for each interrupt is not required.
> > Handle it only if hpd has actually occurred like we handle other
> > interrupts.
> >
> > Signed-off-by: Sonika Jindal <sonika.jindal@xxxxxxxxx>
> > ---
> > Hi,
> >
> > I see we don't check for hotplug_trigger before processing the HPD for any of the platform. Is there any reason for this?
> > For SKL, if I let write to PCH_PORT_HOTPLUG happen for all interrupts, somehow this register gets an invalid value at one point and it zeroes it out.
> > If I put this check before handling HPD, hotplug behaves fine.
> > Please let me know if you see any issue with this approach.
>
> Nice find, this sounds really intrigueing, at least for cpt/ibx platforms.
> I'm not sure whether what will happen with atom/i9xx platforms though
> since the irq bits are different there. But at least bxt has a FIXME
> comment that suggest we do need to save the sticky bits on those platforms
> too.
>
> If we can fix this up for all platforms then I think a subsequent patch
> could try to re-enable the hpd checks in the hdmi ->detect function and
> make use spec compliant. Then after maybe 1-2 kernel releases of testing
> we'll know whether it really works.
>
> But I'd really want to enable this everywhere just to have maximal test
> coverage - we did have reports on all platforms so it seems a generic
> issue.
I think only cpt/ibx suffer from this. Bxt already set port_hotplug_stat 
only when hpd occurs.
Is there a process to get this checked on all platforms, which the fix I 
suggested?
I can only test on SKL as of now.

Regards,
Sonika
> Thanks, Daniel
>
> > Thanks,
> > Sonika
> >
> >   drivers/gpu/drm/i915/i915_irq.c |   11 ++++++-----
> >   1 file changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index a6fbe64..2d47372 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -1760,11 +1760,12 @@ static void cpt_irq_handler(struct drm_device *dev, u32 pch_iir)
> >   	u32 dig_hotplug_reg;
> >   	u32 pin_mask, long_mask;
> >
> > -	dig_hotplug_reg = I915_READ(PCH_PORT_HOTPLUG);
> > -	I915_WRITE(PCH_PORT_HOTPLUG, dig_hotplug_reg);
> > -
> > -	pch_get_hpd_pins(&pin_mask, &long_mask, hotplug_trigger, dig_hotplug_reg, hpd_cpt);
> > -	intel_hpd_irq_handler(dev, pin_mask, long_mask);
> > +	if (hotplug_trigger) {
> > +		dig_hotplug_reg = I915_READ(PCH_PORT_HOTPLUG);
> > +		I915_WRITE(PCH_PORT_HOTPLUG, dig_hotplug_reg);
> > +		pch_get_hpd_pins(&pin_mask, &long_mask, hotplug_trigger, dig_hotplug_reg, hpd_cpt);
> > +		intel_hpd_irq_handler(dev, pin_mask, long_mask);
> > +	}
> >
> >   	if (pch_iir & SDE_AUDIO_POWER_MASK_CPT) {
> >   		int port = ffs((pch_iir & SDE_AUDIO_POWER_MASK_CPT) >>
> > --
> > 1.7.10.4
> >
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